This is the first prospective, multi-center, double-blinded, randomized controlled study of a microbiota suspension derived from intestinal microbes. Patients who have had at least two recurrences of C. difficile infection (CDI) after a primary episode and have completed at least two rounds of standard-of-care oral antibiotic therapy or have had at least two episodes of severe CDI resulting in hospitalization may be eligible for the study. Patients whose CDI returns in less than 8 weeks after the last assigned study treatment may be eligible to receive up to 2 treatments with RBX2660 in the open-label portion of the study.